GROUND-BASED EXTINCTION MEASUREMENTS FOR THE EVALUATION, SPECTRAL BEHAVIOR AND COMPARATIVE ANALYSIS OF THE AEROSOL ε ANGSTROEM COEFFICIENT TO SeaWIFS APLICATIONS IN THE GULF OF CADIZ (SPAIN)

摘要

Sea Color algorithms present great discrepancies in the estimations of pigment concentration in coastal zones (water case 2). As part of calibration/validation and atmospheric correction procedures of sea color applications, special algorithms need to be adapted for regional coastal zones, hence in situ aerosol measurements are required. An operational aerosol database from spectroradiometer measurements is being developed under Spanish project ESP97-1717-CO2-02 for ocean color satellite sensor application in the regional area of the Gulf of Cadiz (Spain). A total characterization of optical aerosol properties: aerosol optical depth (AOD), particle size distribution and radiative aerosol parameters, etc., is being carried out in order to develop and validate operational atmospheric correction algorithms. Auxiliary data as ozone measurements, pressure and wind speed are also available. Here we present a work applied to the SeaWIFS ocean color sensor atmospheric corrections in our area of study, based on ground aerosol measurements. Determination and spectral behavior of the Angstroem ε coefficient have been analyzed using the measured aerosol optical depth. The results show the general spectral features of this coefficient, which is the key parameter in the current worldwide SeaWIFS atmospheric correction algorithm. The variation of the ε (765/865) from the period 96-99 is analyzed here, together with those of the α turbidity Angstroem parameter. For specific and characteristic days of our database a detailed analysis of the spectral behavior of ε is also carried out. Correlations between the aerosol optical depth at the different SeaWIFS sensor bands were also established.